I recently spent three days in Paris on the way home from a conference, becoming just the latest in a long history of visitors to fall in love with the City of Light. It wasn't the sights, the cafes, or the croissants that got me—although all those things helped. It was Vélib', the efficient Parisian bike-sharing network, that really captured my heart.

For a measly 1.70 €, or $2.34, a day, I had a bicycle at my disposal just about anytime I wanted one. And when I didn't want one—when it was raining, for instance—I could forget about cycling and change my transit plans on the fly, which is not an option when I ride my own bike around New York City.

The Vélib' system is simple: Pay the small access fee at a machine to get a 24-hour access code. (One caveat: The machines could not, or would not, read my U.S. credit cards, a problem that other travelers have encountered as well. Luckily I had a European traveling companion—with a European bank card—to bail me out.) With that code, you can then check out a bike at any of the 1,800 Vélib' stands across the city. Long-term subscribers (one year is 29 €, or about $40) get an RFID card that speeds the checkout process. Each bike has an electronic dock securing it in place; once you enter your code or brandish your RFID card, you can release the bike and ride off. You then have 30 minutes of free cycling to reach your destination; assuming that there is another Vélib' stand nearby (and in my experience there always is), you find a vacant slot and dock the bike. If you exceed 30 minutes, which I did only once, you incur a small usage fee of 1 €, or $1.38. That sure beats cab fare.

Central Paris is fairly compact, and having a bike really opened it up to exploration. In three days I used the Métro only twice; otherwise I saw the city by bike. The great thing about cycling as a tourist is that you never stop seeing things. In getting from point A to point B, you inevitably stumble across some exhilarating surprise along the way—look, it's the Arc de Triomphe!—that you would have missed belowground.

Vélib' is utterly inescapable, which is what makes it work so well. Paris has 20,000 shared bikes at its 1,800 stands, according to the Vélib' Web site, and the stands are spaced about 300 meters apart. The system's density is so great that a novice does not need any help in finding bikes. Even without a map or a smartphone, my friend and I rarely failed to find a stand of gray cruisers standing at the ready, just by walking a few blocks while keeping an eye out for the glowing LEDs of the bike stands. We were forced to consult a map of the Vélib' stands just once, as we descended from hilly Montmartre, where we found stand after stand to be vacant. It seemed people were plenty willing to ride the bikes down from Montmartre but not so keen to ride up the hill. Vélib' compensates for this problem somewhat by granting users a 15-minute extension to free riding if they return a bike to an elevated station.

The sturdy three-speed Vélib' bike, with a basket on the front, is optimized for practicality and durability, if not for performance. Compared to the pared-down 1980s Schwinn I ride around New York City, the Vélib' bikes felt awfully heavy and pretty darn slow, but they are easy enough to ride and seemed to weather the elements and the strain of frequent use pretty well. Occasionally I came across a bike with a flat tire, but for the most part they were in working order.

Vélib' was very useful, not to mention novel, for a tourist such as myself, but it was also well-used by Parisians. I did not keep count, but I would estimate that at least half of the cyclists I saw in Paris—and I saw many hundreds if not thousands—were riding shared bikes. The upside of a well-used bike share is that having more cyclists on the road makes cycling safer overall because motorists are more aware of cyclists' presence. The well-publicized "safety in numbers" theory, outlined by public health consultant Peter Jacobsen in Injury Prevention in 2003, has certainly held true in New York City, where cycling injuries and fatalities have tailed off even as the number of cyclists has soared. Anecdotally I would say it looks to apply to Paris as well, where (with the exception of a few aggressive scooter riders) motorists seemed generally more aware and respectful of cyclists than I am accustomed to in cities where there are fewer cyclists.

From a safety standpoint, the major downside of a city where cycling is casual—where one need not commit to biking when leaving the house—is that few riders wear helmets. At least every bike has front and rear lights and a bell.

All told, my Vélib' experience led me to believe that bike sharing, done right, is a potentially transformative addition to civic life. It provides an inexpensive, practical and climate-friendly supplement to public transportation. I'm eager to see how the 1,100-bike Capital Bikeshare in Washington, D.C., which launched in 2010, fares, and I'll watch with interest as numerous other American cities work out the details of their own programs. New York City is preparing to launch its own bike share next year, which will comprise 10,000 bikes at 600 bike-checkout kiosks whose locations have not been finalized, according to The New York Times.

I hope that New York's bike share will reach the critical density that makes the system truly practical, rather than just a novelty for the enthusiastic few. In order for a bike share to really take off, I suspect, the system will need a density comparable to that in Paris, where a bike is always just a short walk away, and just about any destination—whether for sightseeing, commuting or running errands—will have a drop-off point nearby. Given the blowback over new bike lanes, I imagine it will be a challenge to find a politically palatable way to impose new infrastructure on that scale in New York's narrow, crowded streets and sidewalks. But I applaud the ambitious effort and look forward to the day that I can hop on a shared bike for a quick trip across town, and when I can share the road with tourists seeing the city in the same exhilarating way that I got to explore Paris.